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Transform OR clauses to ANY expression

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Replace (expr op C1) OR (expr op C2) ... with expr op ANY(ARRAY[C1, C2, ...])
on the preliminary stage of optimization when we are still working with the
expression tree.

Here Cn is a n-th constant expression, 'expr' is non-constant expression, 'op'
is an operator which returns boolean result and has a commuter (for the case
of reverse order of constant and non-constant parts of the expression,
like 'Cn op expr').

Sometimes it can lead to not optimal plan.  This is why there is a
or_to_any_transform_limit GUC.  It specifies a threshold value of length of
arguments in an OR expression that triggers the OR-to-ANY transformation.
Generally, more groupable OR arguments mean that transformation will be more
likely to win than to lose.

Discussion: https://postgr.es/m/567ED6CA.2040504%40sigaev.ru
Author: Alena Rybakina <lena.ribackina@yandex.ru>
Author: Andrey Lepikhov <a.lepikhov@postgrespro.ru>
Reviewed-by: Peter Geoghegan <pg@bowt.ie>
Reviewed-by: Ranier Vilela <ranier.vf@gmail.com>
Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Jian He <jian.universality@gmail.com>
This commit is contained in:
Alexander Korotkov
2024-04-08 01:27:28 +03:00
parent 75a47b6a0d
commit 72bd38cc99
14 changed files with 785 additions and 20 deletions
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57
doc/src/sgml/config.sgml
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@ -6304,6 +6304,63 @@ SELECT * FROM parent WHERE key = 2400;
</listitem>
</varlistentry>
<varlistentry id="guc-or-to-any-transform-limit" xreflabel="or_to_any_transform_limit">
<term><varname>or_to_any_transform_limit</varname> (<type>boolean</type>)
<indexterm>
<primary><varname>or_to_any_transform_limit</varname> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
Sets the minimum length of arguments in an <literal>OR</literal>
expression exceeding which planner will try to lookup and group
multiple similar <literal>OR</literal> expressions to
<literal>ANY</literal> (<xref linkend="functions-comparisons-any-some"/>)
expressions. The grouping technique of this transformation is based
on the equivalence of variable sides. One side of such an expression
must be a constant clause, and the other must contain a variable
clause. The default value is <literal>5</literal>. The value of
<literal>-1</literal> completely disables the transformation.
</para>
<para>
The advantage of this <literal>OR-to-ANY</literal> transformation is
faster query planning and execution. In certain cases, this
transformation also leads to more effective plans containing
a single index scan instead of multiple bitmap scans. However, it
may also cause a planning regression when distinct
<literal>OR</literal> arguments are better to match to distinct indexes.
This may happen when they have different matching partial indexes or
have different distributions of other columns used in the query.
Generally, more groupable <literal>OR</literal> arguments mean that
transformation will be more likely to win than to lose.
</para>
<para>
For example, this query has its set of five <literal>OR</literal>
expressions transformed to <literal>ANY</literal> with the default
value of <varname>or_to_any_transform_limit</varname>. But not with
the increased value.
<programlisting>
# EXPLAIN SELECT * FROM tbl WHERE key = 1 OR key = 2 OR key = 3 OR key = 4 OR key = 5;
QUERY PLAN
-----------------------------------------------------
Seq Scan on tbl (cost=0.00..51.44 rows=64 width=4)
Filter: (key = ANY ('{1,2,3,4,5}'::integer[]))
(2 rows)
# SET or_to_any_transform_limit = 6;
SET
# EXPLAIN SELECT * FROM tbl WHERE key = 1 OR key = 2 OR key = 3 OR key = 4 OR key = 5;
QUERY PLAN
---------------------------------------------------------------------------
Seq Scan on tbl (cost=0.00..67.38 rows=63 width=4)
Filter: ((key = 1) OR (key = 2) OR (key = 3) OR (key = 4) OR (key = 5))
(2 rows)
</programlisting>
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-plan-cache-mode" xreflabel="plan_cache_mode">
<term><varname>plan_cache_mode</varname> (<type>enum</type>)
<indexterm>